Process of hardening metallic surfaces.



J. H. REID.

PROCESS 0F HARDENING METALLIG SURPAGES.

APPLICATION FILED Imm, 1909. BBNBWBD JAN. 2s, 1910.

Patented Aug. 2, 1910.

rmvmrz'on J. H. nam

. f/f ///.M//

FIG-.5

W1' TN'ESS'ES UNrTap sTATEs JAMES HENRY REID, OF

PATENT oFFrcE.

NEWARK, NEW JERSEY, ASSIGNOR OF ONE-HALF TO GEORGE GOODWIN, OE OTTAWA,CANADA.

PROCESS OF HARDENING METALLIC SURFACES.

Specication of Letters Patent.

Patented Aug. 2, 1910.

Application filed February 3, 1909, Serial No. 475,906. Renewed January26, 1910. Serial No. 540,273.

which an increased degree of surface hardness may be obtained in aminimum time and also to combine with the said process, a method ofgradually annealing or softening the metal below the surface inproportion to the distance therefrom, thereby forming a hardened surfacewith a gradually softened or annealed backing.

The invention is applicable with great advantage to the manufacture ofarmor plates, rails and car wheels, as in these it is desirable to havean extremely hard surface in combination with a gradually softenedbacking, whereby the metal may be utilized to the greatest advantage toresist the stress.

In the manufacture of armor plates as at present carried out, variouscementation processes have been employed, which consist, in general, ofheating the plate in contact with a mixture containing carbon, and insome cases the back of the plate has been cooled. It is also known toseparately apply -hardening material to the surface of the plate throughthe medium of an electric arc directed thereagainst. In these, however,while vthe surface is hardened, the backing is left unaffected and`there is liable to be a more or less sharp separation between thehardened and unhardened plate.

According to the present process, the change from the hardened to theunhardened plate is graduated thereby securin maximum efficiency, and inthe case oarmor plate, offering the greatest possible resistance to thepassage of the projectile.

In carrying out the process, the plate or other article is bedded insuitable granular conducting material, such as hematite, mag

r netite or carbon in the form of coke, a bath of hardening substancesis formed on the surface and an electric current passed through thebath, plate or article and bed. rlhe granularmaterial oHering resistanceto i the flow of the current is raised in temperature, heating the lowerpart of the plate and annealing the same, while the hardening materialscontained in the bath, which may be vanadium, tungsten Aor molybdenum,combine with the surface to hardeny the same.

It may here be observed that the word bath as employed in the presentspecification is intended to ,cover the application of hardeningmaterial in any form to the surface, whether applied directly or throughthe medium of a liquid, gaseous or solid conveyer. I have found,however, that a uid bath, either liquid or gaseous, is more desirable,as the hardening elements can be more uniformly distributed through thesame.

The process is described in detail in the accompanying specificationsand drawings together with various apparatus which may be used'to carryout the same. l'

Referring to the drawings, Figure 1 is a vertical section through oneform of apparatus for treating armor plate. Fig. 2 is a vertical sectionthrough an alternative form. Fig. 3 is a transverse section through amodified form adapted to treat rails to harden the tread surfacethereof. Fig. 4c is the apparatus of Fig. 3 in which a bath of granularsubstance is employed.

In the drawings, like letters of reference indicate corresponding partsin each fi re.

Referring, first, to the apparatus llus trated in Fig. A1, the steelplate A is located within a casing B of suitable conducting material,preferably metallic, and held in suspensin therein, by suitable supportsau and b of non-conducting material. The space around the bottom andpart way u the sides of the plate is filled with a bed of materialadapted to afford resistance to the passage of an electric current ando'f such a character as will not carbonize the surface of the plate,when raised to the anhealing temperature during the carrying out halfwaypp the sides of the plate and the remainder of the sides are protectedfrom the heat by a surrounding band of heat insulating character. In theembodiment illustrated in Fig. l, this band is formed of a wall D of rebrick preferably externally Glazed. L.Jiiibove the plate A a pluralityof elec-. trodes E are provided, suitably supported. as from a plate Fand insulated therefrom. In the embodiment illustrated in Fig. l, meansare provided for forcing the plate F downwardly to exert a pressure onthe bath, which bath, in this case, may be in the form of gas. rIhesemeans comprise a hydraulic piston and cylinder G of suitable and wellknown construction, connected to the plate F. A valved conduit H extendsthrough the portion of the said wall above the plate to permit of theintroduction of the gas or liquid adapted to form the bath at the to ofthe plate. rI`he electrodes E are all united by suitable conductors cand d, which lead to one side of a dynamo, or other source of electricalpower, the opposite side of which is placed in communication with thebed C. Ihis may be accomplished b connecting the said source of powerdirect y with the casing B, but, if desired, and as shown in Fig. 1,plates e, f and g may be provided on the inside of the casing, which areconnected to conductors h, z' and y'.

To prevent over-heating of the casing B, water circulating coils Ic maybe provided therein, the different parts of the coils eX- tending aroundthe heat insulating bands andthe remainder of the sides beingpreferably, separately controlled.

In the form of apparatus villustrated in Fig. 2, the heat insulatingband is in the form of a dead air space Z, providedfaround the upperportion of the sides of the plate.

The conductor m is connected directly to the casing B and the hydraulicpiston and cylinder are omitted. -The bath, shown in the form of aliquid, is introduced through the valved conduit H.

In the embodiment illustrated in Fig. 3, two blocks I and .I of heatinsulating material, such as fire-brick or fire-clay, are formed andadapted to extend around the upper part of the sides of the rail, andthe inside of the upper part of the casing B, and bein centrallyrecessed, whereby a basin K will be provided on top of the rail toreceive the bath. The bath in this case, \is shown in the form of aliquid and the cover L resting on the liquid forms one of the electrodesto which the conductor o is connected, the opposite conductor p beingconnected directly to the casing B.

The form of apparatus illustrated in Fig. 4 is the same as that shown inFig. 3, only a granular bath is shown in place of the li uid one.

n carrying out the process, the plate or @saisi article is bedded on theelectrical conducting and resisting material, the bath is formed on thesurface and the current sent through the bath, plate or article and bed.

The resistance odered by the material forming the bed will raise thelower part of the plate to a moderate heat and care must be taken toalways keep the temperature below the critical temperature of theparticular steel being worked, whereby the absorption of any carbon bythe steel will be prevented and its original properties will beuntouched. To do this with ordinary steel, it is necessary that themaximum temperature should not go much over 560 C. and if there is atendency for the plate to heat over this temperature, it will benecessary to use the water circulating coils illustrated in Fig. 1 toreduce the temperature. Should it become necessary to work a steel at ahigher temperature than about 5500, it will `be necessary inmanufacturing the steel, to incorporate such materials as will raise itscritical point below atmospheric conditions. This can be done byalloying the steel with vanadium, tungsten or molybdenum.

The bath on the surface of the steel to toughen and harden the same maybe either in the form of a liquid, a gas or a granular or solid mixture,and will contain various lhardening elements, such as nickel, chromium,vanadium, carbon, tungsten Vor m01- ybdenum, either alone or incombination. The liquid or gaseous bath, however, is most desirable asit insures a more uniform distribution of the hardening elements.

The form of apparatus shown in Fig. l is that which would be bestadaptedfor utilizing a gaseous bath applied under pressure, such as. carbonmonoXid. If this gas were used under pressure, the electric currentpassing through it would form arcs on the surface of the steel and wouldcause the gas -to give up carbon to the steel, thereby hardening andtoughening the same.

rIhe liquid bath may be formed of a carbon carrying oil and may containvarious hardening metals before specified or salts of them. lIhehardening bath might alsobe formed by placing the hardening elements onthe surface of the steel prior to the passage of the electric currentand on passage of the same arcs would be formed on the surface of thesteel fusing or -heating hardening elements and thus incorporating themwith the surface of the steel.

The temperature of the steel will generally, be a maximum at the surfacein contact with the hardening bath, being raised to this temperatureeither through the direct heat of the electric arc, or through the bath,the temperature of which is raised by the arc playing on it or theelectric current passing through it.4 From the surface being hardcned,the temperature gradually decreasesV soi-bed suflicientof the to theopposite surface in contact with the heated bed of material, whosetemperature is below the critical temperatune of the steel as hereinexplained.

The process is continued in operation until the steel has been deemed tohave abharde'ning materials and the electric current -is then shut olfand the steel preferably, allowed to cool gradually thereby providingagainst the tendency to change its physical pro erties.

The intensity of the action can e regulated by the density of thecurrent and by the period of exposure. The hardening and toughening ofthe plate will be gradual, working from the surface downward and thedepth of hardening can be controlled by the heat of the material ofwhich the bed is formed.

By this method, a plate or article will be obtained which will beextremely hard and tough on the surface, but will become more .'luctileand malleable and possessing a greater degree of elasticity as the backof the plate is reached.

The means for exerting a pressure shown in Fig. 1, may be used with aliuid or solid as well as a gaseous bath, the e ect being to force thehardening element into the metal and facilitate their amalgamation. Itmight also be observed that when the granular or solid form of bath isused, it is not essential that the arcs should actually fuse thehardening elements, as experience has shown that absorptionI will takeplace on the part of the steel, even when the temperature isconsiderably below the fusing point. It will therefore, be understoodthat the bath of hardening elements might simply be heated by thepassage of electric current or by the arcs directed against the same.

What I claim as my invention is l. A process of treating metallicsurfaces which consists in applying a fluid bath containing hardeningelements to the surface and passing an electric current through thefluid bath and the plate, said bath being in a fluid state before thecurrent is applied.

2. The herein descritd process of hardening metallic plates or articles,which consists in bedding the plate or article in granular conductingmaterial, applying a hardening bath to the exposed side of the plate orarticle while insulating the bath from the bed, and passing an electriccurrent through the bath, plate or article, and the bed.

3. The herein Vdescribed process of treating metallic plates orxarticles which consists in embedding the plate or article in granularconducting material, applying a bath to the surface containing hardeningmetals and passin an electric current through the hardening bath, theplate or article, and the conducting material.

4. The process of treating previously formed metallic plates or articleswhich consists in bedding part of the plate or article ina materialwhich affords resistance to the passage of the electric current andwhich will not combine with the metal of the plate or article, ap lyingtreating substances to the surface o thelarticle and passing an electriccurrent through the treating substance, plate Orarticle and bed ofresistant material. L

5. The herein described process of treating metallic plates or articleswhich consists in bedding the bottom and part of the sides of the plateor article yin material adapted t'o adord resistance to, the passage ofan electric current and to be heated thereby the said material being ofsuch character as not to combine with the plate or article, applying abath containing hardening materials tothe exposed surface of the plateor article, suitable insulation being provided on the sides of the plateor article between the bath and the bed,and then passing an electriccurrent through the bath, the plate or article and the bed.

6. The herein described process of treating metallic plates or articleswhich consists in embedding the plate or article in granular conductingmaterial which will not combine with themetal of the plate or article,applying a hardening bath to the surface and passing an electric currentthrough the hardening bath, the plate or article and the conductingmaterial.

7. The herein described process of treating metallic plates or articleswhich consists in embedding the plate or article in hematite, applying ahardening bath to the surface and passing an electric current throughthe hardening bath, the plate or article and the conducting material. y

8. The process of treating a metallic surface to harden the same, whichconsists in applying a hardening bath under pressure to the surface andpassing an electric cui'- `rent`through both the bath and plate orarticle being treated, whereby both the bath and plate or article willbe heated bythe passage of` the` current. A

9. The herein described process of treating metallic plates or articleswhich consists in embedding the plate in electrically conducting andresisting material, applying a bath to the surface containing hardeningmetals, and passing an electric current through the hardening bath, theplate or article and the conducting material.

In witness whereof I' have hereunto set my hand in the presence .of twowitnesses. JAMES HENRY REID. Witnesses:

RUSSEL S. SMART, WM. A. WYMAN.

